Self-limiting wear contact pad slider and method for making the same

ABSTRACT

The present invention provides a non-actuatable, self-limiting wear contact pad slider and method for making the same. A protruding element surrounding the transducer is fabricated using a third etch step so that the protruding element has a height that is greater than or equal to the designed fly height of the aerodynamic lift surface minus the disk roughness.

RELATED PATENT DOCUMENTS

[0001] This is a divisional of patent application Ser. No. 09/687,234,filed on Oct. 13, 2000 (SJO0000026US01), to which Applicant claimspriority under 35 U.S.C. §120.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates in general to data storage systems, andmore particularly to a self-limiting wear contact pad slider and methodfor making the same.

[0004] 2. Description of Related Art

[0005] Fixed magnetic disk systems, typically referred to as “hard” diskdrives, are now commonplace as the main non-volatile storage in modempersonal computers, workstations, and portable computers. Such hard diskdrives are now capable of storing gigabyte quantities of digital data,even when implemented in portable computers of the so-called “notebook”class. Many important advances have been made in recent years that haveenabled higher data density and thus larger storage capacities of harddisk drives, and that have also enabled much faster access speeds, bothin the bandwidth of data communicated to and from the hard disk drive,and also in the access time of specified disk sectors. Advances havealso been made that have greatly reduced the size and weight of harddisk drives, particularly as applied to portable computers, have beenmade over recent years. These advances have resulted in the widespreadavailability of ultra-light portable computers, yet having state-of-theart capability and performance.

[0006] A head/disk assembly typically comprises one or more commonlydriven magnetic disks rotatable about a common spindle and cooperatingwith at least one head actuator for moving a plurality of transducersradially relative to the disks so as to provide for the reading and/orwriting of data on selected circular tracks provided on the disks. Themagnetic transducer or “head” is suspended in close proximity to arecording medium, e.g., a magnetic disk having a plurality of concentrictracks. The transducer is supported by an air bearing slider mounted toa flexible suspension. The suspension, in turn, is attached to apositioning actuator.

[0007] During normal operation, relative motion is provided between thehead and the recording medium as the actuator dynamically positions thehead over a desired track. The relative movement provides an air flowalong the surface of the slider facing the medium, creating a liftingforce. The lifting force is counterbalanced by a predeterminedsuspension load so that the slider is supported on a cushion of air. Airflow enters the leading edge of the slider and exits from the trailingend. The head resides toward the trailing end, which tends to fly closerto the recording surface than the leading edge.

[0008] The recording medium holds information encoded in the form ofmagnetic transitions. The information capacity, or areal density, of themedium is determined by the transducer's ability to sense and writedistinguishable transitions. An important factor affecting areal densityis the distance between the transducer and the recording surface,referred to as the fly height. It is desirable to fly the transducervery close to the medium to enhance transition detection. Some flyheight stability is achieved with proper suspension loading and byshaping the air bearing slider surface (ABS) for desirable aerodynamiccharacteristics.

[0009] Another important factor affecting fly height is the slider'sresistance to changing conditions. If the transducer fly height does notstay constant during changing conditions, data transfer between thetransducer and the recording medium may be adversely affected. Flyheight is further affected by physical characteristics of the slidersuch as the shape of the ABS. Careful rail shaping, for example, willprovide some resistance to changes in air flow.

[0010] Hard drive manufacturers are starting to incorporate proximityrecording type sliders in drives in order to achieve higher storagedensities. The proximity recording slider is designed to maintain asmall area near the read-write element in constant contact with thedisk, and thus enabling smaller bit size and ultimately larger storagedensities. This approach to increasing storage density puts considerableamount of strain on controlling wear at the slider-disk interface,because a slight variation in contact load and contact area couldgreatly affect the drive survivability.

[0011] Slider-disk contact results in lubricant depletion anddegradation, wear of both surfaces, generation of wear particles,stick-slip, etc. All these phenomena affect magnetic performance of thedisk drive, e.g., through jitter, as well as its durability.Nevertheless, as mentioned above, a contact slider is key forhigh-density magnetic recording.

[0012] As product fly heights are getting closer to the disk to increaseareal density, the ultimate fly height goal will be to put the elementin contact with the disk media, thus reducing the fly height to zero.However in practice, a reliable contact interface is very difficult toachieve due to the wear of the head and disk, resulting in early failurewhen compared to higher fly heights with a cushion of air between them.The reliability problem is exacerbated by manufacturing tolerances whichresults in significant variation in the amount of interference in thecontact interface. Even with a product design point centered nominallyat zero fly height or contact, manufacturing tolerances for both diskroughness and head fly height result in a distribution of interferencesuch that half the interfaces will have negative (i.e., too much)interference and wear out prematurely and the other half will havepositive (i.e., too little) interference and fly with an air separationwhich will cause poor magnetic performance.

[0013] U.S. Pat. No. 5,761,003, entitled “Magnetic head slider withcrown ABS”, issued Jun. 2, 1998, to Toshiharu Sata, which is assigned toCitizen Watch Co., Ltd., and which is incorporated by reference herein,discloses a magnetic head slider including a crown air-bearing surface(ABS) adapted to be located opposite to a magnetic disk. The ABSincludes a rear pad with a convexly curved upper surface, arranged at acenter of the air-discharging end and longitudinally spaced from theboundary. The rear pad has such a small dimension that a dynamicpressure due to the air introduced onto the ABS is hardly applied to therear pad. However, the slider design is not made to fly in contact withthe disk such that the interference is zero over a wide range ofmanufacturing tolerances.

[0014] One slider design that attempts to achieve contact recording isdisclosed in “An Active Slider For Practical Contact Recording”, IEEETransactions On Magnetics, Vol. 26, No. 5, September 1990, pp.2478-2483, by C. E. Yeak-Scranton et at. (herein referred to as “ActiveSlider article”). In the “Active Slider article” active material islaminated into a thin-film head to form an actuatable bender at thetrailing end of the slider. The actuatable area allows the recordinghead to be raised or lower thereby providing contact recording whenneeded, but preventing rapid failure of the interface.

[0015] Nevertheless, the design is complex because it requires not onlyadditional processing steps to add the laminated active material, butalso additional circuitry to coritrol and supply the bender drivevoltage.

[0016] It can be seen then that there is a need for a simple head designthat can be made to fly in contact with the disk such that theinterference is zero over a wide range of manufacturing tolerances.

SUMMARY OF THE INVENTION

[0017] To overcome the limitations in the prior art described above, andto overcome other limitations that will become apparent upon reading andunderstanding the present specification, the present invention disclosesa self-limiting wear contact pad slider and method for making the same.

[0018] The present invention solves the above-described problems byfabricating a protruding element surrounding the transducer using athird etch step so that the protruding element has a height that isgreater than or equal to the designed fly height of the aerodynamic liftsurface minus the disk roughness.

[0019] A slider in accordance with the principles of the presentinvention includes a support structure having a leading and a trailingedge relative to the motion of the recording medium and an air bearingstructure positioned on the support structure extending to the trailingedge of the support structure, the air bearing structure having an airbearing surface and a non-actuatable, wearable pad positioned at thetrailing end of the air bearing structure and extending above the airbearing surface, the air bearing surface being formed to provide adesired fly height and the wearable pad having a surface area of lessthan 5% of a total air bearing surface area and a predetermined heightso that wearing of the pad during use produces an interference of zeroat the desired fly height and provides negligible lift to the slider.

[0020] Other embodiments of a slider in accordance with the principlesof the invention may include alternative or optional additional aspects.One such aspect of the present invention is that the air bearing surfacefurther comprises at least one aerodynamic lift surface level generatinglift to provide the desired fly height, the non actuatable, wearable padcomprising a last surface level extending above the at least one surfacelevel of the air bearing surface.

[0021] Another aspect of the present invention is that the at least onesurface level further comprises two surface levels.

[0022] Another aspect of the present invention is that thenon-actuatable, wearable pad is formed around a magnetic sensor.

[0023] Another aspect of the present invention is that the air bearingsurface is formed using two etch steps and the non-actuatable, wearablepad is formed using a third etch step.

[0024] Another aspect of the present invention is that the wearable padforms a fourth surface level to the slider.

[0025] Another aspect of the present invention is that the predeterminedheight of the non-actuatable, wearable pad is selected to be greaterthan or equal to the desired fly height minus a disk roughness.

[0026] Another aspect of the present invention is that the sliderfurther includes at least one front air bearing pad.

[0027] Another aspect of the present invention is that the sliderfurther includes side rails extending along sides of the supportstructure.

[0028] Another aspect of the present invention is that thenon-actuatable, wearable pad is formed of a material selected from thegroup comprising alumina, TiC/A12O3 and silicon.

[0029] Another aspect of the present invention is that thenon-actuatable, wearable pad is preferably less than 3.5% and morepreferably less than 2% and a preferred embodiment is 1%.

[0030] In another embodiment of the present invention, a method forforming a slider is provided. The method includes forming a slider bodyhaving a first side, a second side, a leading edge and a trailing edge,using at least a first etching to form an air bearing structure on theslider body extending to the trailing edge for providing a desired flyheight and using a last etching to form a non-actuatable, wearable padon the air bearing structure extending to the trailing edge, thewearable pad extending above the air bearing surface and having asurface area of less than 5% of a total air bearing surface area and apredetermined height so that wearing of the pad during use produces aninterference of zero at the desired fly height and provides negligiblelift to the slider.

[0031] These and various other advantages and features of novelty whichcharacterize the invention are pointed out with particularity in theclaims annexed hereto and form a part hereof. However, for a betterunderstanding of the invention, its advantages, and the objects obtainedby its use, reference should be made to the drawings which form afurther part hereof, and to accompanying descriptive matter, in whichthere are illustrated and described specific examples of an apparatus inaccordance with the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Referring now to the drawings in which like reference numbersrepresent corresponding parts throughout:

[0033]FIG. 1 is a plan view of a disk drive;

[0034]FIG. 2 is a perspective view of an actuator assembly;

[0035]FIG. 3 illustrates a greatly enlarged view of a head gimbalassembly;

[0036]FIG. 4 shows a self-limiting wear contact pad slider according tothe present invention;

[0037]FIG. 5 illustrates a side view of the slider of FIG. 4;

[0038]FIG. 6 illustrates the determination of the height of theprotruding element surrounding the transducer;

[0039]FIG. 7 illustrates the burnish time versus the change in magneticsignal for a slider according to the present invention;

[0040]FIG. 8 illustrates the burnish time versus the increase inelement-to-disk spacing;

[0041]FIGS. 9a-b illustrate the effect of crown on fly heights; and

[0042]FIGS. 10a-b illustrate the self-limiting characteristics of thecontact pad slider according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0043] In the following description of the exemplary embodiment,reference is made to the accompanying drawings which form a part hereof,and in which is shown by way of illustration the specific embodiment inwhich the invention may be practiced. It is to be understood that otherembodiments may be utilized as structural changes may be made withoutdeparting from the scope of the present invention.

[0044] The present invention provides a self-limiting wear contact padslider and method for making the same. A protruding element surroundingthe transducer is fabricated using a third etch step so that theprotruding element has a height that is greater than or equal to thedesigned fly height of the aerodynamic lift surface minus the diskroughness.

[0045]FIG. 1 is a plan view of a disk drive 100. Disk drive 100 includesa disk pack 1 12, which is mounted on a spindle motor (not shown) by adisk clamp 114. Disk pack 112, in one preferred embodiment, includes aplurality of individual disks which are mounted for co-rotation about acentral axis 115. Each disk surface on which data is stored has anassociated head gimbal assembly (HGA) 116 which is mounted to at leastone actuator assembly 118 in disk drive 100. An actuator assembly asshown in FIG. 1 is of the type known as a rotary moving coil actuatorand includes a voice coil motor (VCM) shown generally at 120. A voicecoil motor 120 rotates an actuator assembly 118 with its attached HGAs116 about a pivot axis 121 to position HGAs 116 over desired data trackson the associated disk surfaces, under the control of electroniccircuitry housed within disk drive 100.

[0046] More specifically, an actuator assembly 118 pivots about axis 121to rotate head gimbal assemblies 116 generally along an arc 119 whichcauses each head gimbal assembly 116 to be positioned over a desired oneof the tracks on the surfaces of disks in disk pack 112. HGAs 116 can bemoved from tracks lying on the innermost radius, to tracks lying on theoutermost radius of the disks. Each head gimbal assembly 116 has agimbal which resiliently supports a slider relative to a load beam sothat the slider can follow the topography of the disk. The slider, inturn, includes a transducer which is utilized for encoding fluxreversals on, and reading flux reversals from, the surface of the diskover which it is flying.

[0047]FIG. 2 is a perspective view of an actuator assembly 200. Actuatorassembly 200 includes base portion 222, a plurality of actuator arms226, a plurality of load beams 228, and a plurality of head gimbalassemblies 216. Base portion 222 includes a bore which is, in thepreferred embodiment, coupled for pivotal movement about axis 221.Actuator arms 226 extend from base portion 222 and are each coupled tothe first end of either one or two load beams 228. Load beams 228 eachhave a second end-which is coupled to a head-gimbal assembly-216.According to the present invention, multiple, independently controlledactuator assemblies 200 are provided in a disk drive.

[0048]FIG. 3 illustrates a greatly enlarged view of a head gimbalassembly 300. Head gimbal assembly 300 includes gimbal 330, which has apair of struts 332 and 334, and a gimbal bond tongue 336. Head gimbalassembly 300 also includes slider 338 which has an upper surface 340 anda lower, air bearing surface 342. Transducers 344 are also preferablylocated on a leading edge of slider 338. The particular attachmentbetween slider 338 and gimbal 330 is accomplished in any desired manner.For example, a compliant sheer layer may be coupled between the uppersurface 340 of slider 338 and a lower surface of gimbal bond tongue 336,with an adhesive. A compliant sheer layer permits relative lateralmotion between slider 338 and gimbal bond tongue 336. Also, gimbal bondtongue 336 preferably terminates at a trailing edge of slider 338 with amounting tab 346 which provides a surface at which slider 338 isattached to gimbal bond tongue 336.

[0049] A conventional slider design starts off with a flat polishedsurface, from which a patterned air bearing surface (ABS) is created bya removal process such as etching or ion milling. The ABS surface isalways the top most polished surface and pressurizes with positivepressure to lift the ABS up producing an air cushion above the disk. Airbearing surfaces are formed by single or dual etch processing whichresult in either 2 or 3 surface levels, respectively.

[0050]FIG. 4 shows a self-limiting wear contact pad slider 400 accordingto the present invention. The slider 400 is formed using a dual etchdesign with three surface levels 410-416, wherein a third etch is addedto produce a fourth surface level 420. Accordingly, the top most surfaceis now a small, non-actuatable wearable contact pad 420 around themagnetic element pole tips 422. The self-limiting contact pad 420 iswearable in the sense that it is not formed of a hard overcoat thatprevents wear, but rather exhibits wear when it comes into contact withthe disk surface. This protruding pad 420 is small enough that it doesnot carry any significant amount of load and thus provides negligiblelift to the slider due to its small size. This pad 420 is also smallenough so that it will wear quickly and easily and will not affect thefly height as it wears down, which provides the pad 420 with the abilityto achieve an interference of zero. The slider is simple to constructand is non-actuatable. The slider comprises one or more materialsselected from alumina, TiC/AI₂O₃, or silicon. In addition to the rearpad 420, front pads 416 are formed on side rails 418. The air bearingsurfaces of the wear pad 420 is less than 5% of the total air bearingsurface area, and is preferably less than 3.5% and more preferably lessthan 2%. In fact, a preferred embodiment is 1%.

[0051]FIG. 5 illustrates a side view 500 of the slider of FIG. 4. InFIG. 5, the four levels provided by the three etch steps are clearlyevident. The front air bearing surfaces 510 includes three levels512-516 that are formed using the first two etch steps. The rear airbearing surfaces 530 also include three levels 540-514. The protrudingelement 550 surrounding the transducer 552 is fabricated using a thirdetch step so that the protruding element 550 has a height that isgreater than or equal to the designed fly height of the aerodynamic liftsurface minus the disk roughness.

[0052] The air bearing surfaces 516, 544, which pressurize and carry theload of the slider 500, is now the second highest surface created by thethird etching process. The depth of the third etch produces anon-actuatable protruding pad 550 that is designed to be greater than orequal to the designed fly height of the original ABS surface prior toreceiving this third etch.

[0053]FIG. 6 illustrates the determination of the height of theprotruding element surrounding the transducer. The air bearing surfacesof the slider are selected to provide a fly height of “M”. The roughnessof the disk surfaces is “N”. The difference-between the fly height “M”and the disk surface roughness “N” is calculated to be “X”. Thus, theprotruding element surrounding the transducer is fabricated using athird etch step so that the protruding element has a height “L” that isgreater than or equal to the designed fly height of the aerodynamic liftsurface minus the disk roughness.

[0054] The slider thus flies at a certain fly height “M” and has aprotruding pad of “L” height which will put it in contact with the diskfor a wide range of manufacturing tolerances. When the slider and diskare first put together, the pad will interfere with the disk and willwear down until the interference is zero, at which point, the wear willbe self limiting and not continue further. This is because the airbearing surface continues to support and lift the air bearing at itsdesigned fly height.

[0055] Experiments have shown that this initial wear in process takesplace fairly rapidly. FIG. 7 illustrates a graph 700 of the burnish time710 versus the change in magnetic signal 720 for a slider according tothe present invention. FIG. 7 illustrates that the magnetic signal 730settles within about thirty minutes 740. FIG. 8 illustrates a graph 800the burnish time 810 versus the increase in element-to-disk spacing 820.FIG. 8 shows that the element-to-disk spacing 830 also settles in aboutthirty minutes 840. The end result of this design and burn-in processresults in a head/disk interface which is at contact or zerointerference and which can be reproduced on variety parts with a widerange of manufacturing tolerances.

[0056]FIGS. 9a-b illustrate the effect of crown on fly heights. In orderto be able to adjust the flying height in situ in the disk drive, it isimportant to measure accurately the flying height in the disk drive.Methods for accurately measuring the flying height of the head in a diskdrive are disclosed in U.S. Pat. No. 4,777,544, issued Oct. 1, 1988 toBryon R. Brown et al. and assigned to International Business MachinesCorporation, which is hereby incorporated by reference. In Brown et al.,the amplitude of the magnetic signal at the nominal disk velocity iscompared to the amplitude at the touch down velocity of the slider-diskcombination using the Wallace spacing loss formula. In FIG. 9a, theslider 900 doesn't touch the disk 910 at the location of the element912, but at the lowest point 920, which due the positive crown, is nearthe middle of the slider. The measured flying height (FH-M) 930 is lowerthan the actual spacing (FH-A) 932 between the magnetic element and thedisk, at the nominal disk velocity. This underestimate 940 of thespacing can be several tens of nanometers, making it virtuallyimpossible to determine spacings of 20 or less.

[0057]FIG. 9b illustrates a second embodiment of a self-limiting wearcontact pad slider 950 according to the present invention. In FIG. 9b,the slider design solves this problem. If the height of the protrudingpad 960 is comparable to the nominal positive crown value, on decreasingthe disk velocity the slider 950 will touch the disk at a point on thepad 960 and thus very close to the magnetic head. Knowing the pitchangle of the slider and geometry of the crown, one can select the padheight, so that trailing end pad 960 touches the disk before other partsof the slider.

[0058]FIGS. 10a-b illustrate the self-limiting characteristics of thecontact pad slider according to the present invention. The ABS designcan be optimized to maximize performance without regard to impact onsensitivities to manufacturing tolerances. FIG. 10a illustrates theself-limiting wear contact pad slider with a first higher fly height1000. The protruding element 1010 contacts the surface of the disk 1012during burnishing. The first time the head flies on a 1014 disk, it isburnished by accessing across the disk several times. The protrusion1010 will wear down until the contact force is zero. After burnish 1020,the self-limiting wear contact pad slider exhibits a clearance 1030provided by the self-limiting wear characteristics of the protrudingelement.

[0059]FIG. 10b illustrates the self-limiting wear contact pad sliderwith a second lower fly height 1050. The protruding element 1060 stillcontacts the surface of the disk during burnishing 1014. After burnish1020, the self-limiting wear contact pad slider exhibits the sameclearance 1030 provided as exhibited in FIGS. 10a. Thus, theself-limiting wear contact pad 1060 decouples the ABS design andmanufacturing tolerances from contact force. The self-limiting wearcontact pad slider improves magnetic performance by allowing the removalof recession and the carbon overcoat (COC). A tightly controlled spacingof a few nanometers can be achieved by applying additional wear.

[0060] The foregoing description of the exemplary embodiment of theinvention has been presented for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed. Many modifications andvariations are possible in light of the above teaching. It is intendedthat the scope of the invention be limited not with this detaileddescription, but rather by the claims appended hereto.

What is claimed is:
 1. A method for forming a slider, comprising:forming a slider body having a first side, a second side, a leading edgeand a trailing edge; using at least a first etching to form an airbearing structure on the slider body extending to the trailing edge forproviding a desired fly height, and using a last etching to form anon-actuatable, wearable pad on the air bearing structure extending tothe trailing edge, the wearable pad extending above the air bearingsurface and having a surface area of less than 5% of a total air bearingsurface area and a predetermined height so that wearing of the padduring use produces an interference of zero at the desired fly heightand provides negligible lift to the slider.
 2. The method of claim 1wherein the using at least a first etching to form an air bearingstructure further comprises using two etching to form three surfacelevels.
 3. The method of claim 2 wherein the using a last etching toform a non-actuatable, wearable pad further comprises forming a fourthsurface level.
 4. The method of claim 3 wherein the using a last etchingto form a non-actuatable, wearable pad further comprises forming thenon-actuatable, wearable pad around a magnetic sensor.
 5. The method ofclaim 1 wherein the using a last etching to form a non-actuatable,wearable pad further comprises forming a non-actuatable, wearable padhaving a predetermined height selected to be greater than or equal tothe desired fly height minus a disk roughness.
 6. The method of claim 1further comprising forming at least one front air bearing pad.
 7. Themethod of claim 1 further comprising forming side rails extending alongsides of the support structure.
 8. The method of claim 1 wherein thenon-actuatable, wearable pad is formed of a material selected from thegroup comprising alumina, TiC/AI₂O₃ and silicon.
 9. The method of claim1 wherein the non-actuatable, wearable pad comprises a surface area ofless,than 3.5% of a total air bearing surface area.
 10. The method ofclaim 1 wherein the non-actuatable, wearable pad comprises a surfacearea of less than 2% of a total air bearing surface area.
 11. The methodof claim 1 wherein the non-actuatable, wearable pad comprises a surfacearea of 1% of a total air bearing surface area.